As the number of aircraft continues to increase, greater constraints are being placed upon operation of these aircraft particularly in and around destination points such as airports and instrument landing system marker beacons. These constraints are usually in the form of altitude, heading and airspeed limitations to which the aircraft must closely adhere in order to achieve the required spacing from other aircraft in the area. Around those destinations having a greater density of aircraft, the number of altitude and airspeed constraints may increase. For example, a descending aircraft may have several intermediate altitudes and airspeeds as well as several heading changes during the descent in order to maintain proper spacing from other aircraft.
Coupled with the traffic separation requirements, the high cost of fuel has necessitated that the aircraft be operated as fuel efficiently as possible throughout the flight. In some of the more sophisticated aircraft, such as those flown by commercial airlines, the flight is planned from takeoff to landing to achieve maximum fuel efficiency. Numerous factors such as aircraft gross weight, prevailing winds, assigned cruising altitudes, and distance to destination are computed to arrive at aircraft operating parameters such as takeoff, climb, cruise and descent airspeeds and altitudes which will achieve optimum fuel use while maintaining aircraft safety. In the more sophisticated aircraft, these altitudes and airspeeds are calculated and then stored prior to takeoff in sophisticated aircraft navigational systems which typically include a programmable digital flight computer. The computer provides the pilot with the necessary information to fly the aircraft along the programmed route. When the aircraft is flying on autopilot, this information is relayed to the autopilot system which generates commands to the flight controls to fly the aircraft along the programmed route.
Sometimes however, the aircraft is not permitted to fly the exact route as programmed. Changes to the programmed route of flight may be required during the descent phase of the flight when traffic spacing becomes more precise due to the density of aircraft. Therefore, unplanned heading, altitude and airspeed changes may be required. When these changes require a departure from the programmed flight route, they may be made without the benefit of information concerning optimum descent rates and airspeeds, thereby resulting in increased fuel consumption.
Conventionally, glideslope information has been provided to aircraft in the form of radio signals transmitted from a ground station to the aircraft. These are deciphered by equipment onboard the aircraft to generate a visual display of the aircraft's position relative to the electrically beamed glideslope. Typical aircraft glideslope navigational devices have been disclosed in U.S. Pat. No. 4,012,626 by Miller, et al, which disclosed an air navigation system which generates a pitch command signal for controlling the vertical flight of an aircraft, and which is produced by summing a signal indicative of the vertical displacement of the aircraft from a computed glideslope. The glideslope is computed using data representing the aircraft range from a VORTAC station, aircraft altitude, desired altitude, flight path angle, bias offset and waypoint location.
In U.S. Pat. No. 4,021,009--Baker, et al, there is disclosed an area navigation system having vertical path control wherein a minimum flight path angle is computed using the aircraft altitude, the altitude of a navigational waypoint, and the distance of the aircraft from the navigational waypoint. The aircraft instantaneous flight path angle is compared to the computed minimum flight angle to generate an error signal which is displayed in the aircraft.
Various other aircraft navigational systems have been disclosed which provide information for navigating an aircraft. Foster, U.S. Pat. No. 4,413,322 discloses an area navigation device which automatically establishes guidepoints along a preselected course line intersecting any one of four cardinal radials of a VOR station.
In U.S. Pat. No. 4,220,994--Hendrickson, there is disclosed a microprocessor based system which uses geometrical relationships to assist in aircraft navigation.
In U.S. Pat. No. 2,671,621--Schuck, there is disclosed a navigation system which provides a number of nonconverging electronic guide paths.
Apparatus and methods for continuous computation of a course line from an aircraft to a destination point are disclosed in U.S. Pat. No. 3,581,073 by Visher.
Kreeger, U.S. Pat. No. 3,899,662 discloses a CRT for displaying to the pilot the position and motion of the aircraft relative to ground references and terrain features.
U.S. Pat. No. 3,919,529 by Baker, et al, discloses a radio navigation system utilizing navigational data for the generation of aircraft positional information with respect to a radar guidance transmitter system.
Apparatus for combining positional data from VOR/DME radio navigation systems with data derived from an OMEGA receiver is disclosed in U.S. Pat. No. 3,941,983.
In U.S. Pat. No. 3,994,456--Post, et al, there is disclosed control apparatus for an aircraft navigation system which computes a curved path between two courses.
Narveson, U.S. Pat. No. 4,070,662 discloses a display generator for generating video signals at a CRT screen.
U.S. Pat. No. 4,086,632--Lions, discloses a slew control to generate guidepoints on a computer based CRT map display unit.
The following U.S. patents disclose various aircraft navigational systems comprising principally electronic hardware adapted to create guidepoints for aircraft navigation: U.S. Pat. No. 4,283,705; U.S. Pat. No. 4,212,067; U.S. Pat. No. 4,069,412; U.S. Pat. No. 3,838,427; U.S. Pat. No. 3,831,010; U.S. Pat. No. 3,803,611; U.S. Pat. No. 3,778,601; U.S. Pat. No. 3,796,867; U.S. Pat. No. 3,750,942; U.S. Pat. No. 3,696,671; U.S. Pat. No. 3,659,291; U.S. Pat. No. 3,644,928; U.S. Pat. No. 3,696,426; U.S. Pat. No. 3,652,837; U.S. Pat. No. 3,621,211; U.S. Pat. No. 3,500,413; U.S. Pat. No. 3,486,815; U.S. Pat. No. 3,534,399; U.S. Pat. No. 3,234,552; and U.S. Pat. No. 3,140,391.